Circular boring or milling tools of large diameter and operating under high power are used, for example, to make circular openings in concrete walls, rock faces or the like. Couplers are usually used to couple the drive shaft of a drive apparatus to the tools themselves. A problem arises with such couplers that transfer of the high power and high torque between releasable elements is difficult since the driving and driven elements of the couplers have a tendency to freeze or jam together so that replacement of the cutter tool by another one, for example with fresh cutting elements thereon, or of a different size, becomes difficult. Release of such couplers, thus, causes problems which cannot be readily solved. Forces necessary to release such couplers may lead to a deformation of the usually internally hollow or cylindrical cutting tools, rendering them useless for sharpening or further use. Interchange of cutters, when the parts have frozen or jammed together, is time-consuming and difficult, particularly when the coupling must be loosened on a job, remote from a shop; further, specialty tools to effect release are frequently not available at job sites where the cutters are to be used.
The couplers must meet another requirement, namely that they can be easily reassembled. One of the coupling elements, for example the one coupled to a driving machine or motor, is frequently fixedly secured to the drive shaft of the machine. The coupling element attached to the cutting tool, however, is portable. To assemble the cutting tool with its coupler part on the coupler of the drive machine must be so simple that experimentation and search for an appropriate seating position is simple. The association of the releasable tool element from the drive shaft, both with respect to angular as well as axial position, must therefore be simple and positive, without requiring special steps or procedures to match the respective coupling elements together. The system should, further, be so simple that it can be operated even by only marginally skilled personnel who may be good stoneworkers, but poor machine mechanics.